1. Field of the Invention
The present invention relates to an optical disk recording apparatus, and more specifically to the power optimization of a light-emitting source used in an illumination system for an optical disk recording apparatus capable of recording data into an optical disk as an optical storage medium and of reproducing the recorded data.
2. Description of the Related Art
Traditionally, it is known that an optical disk is capable of recording the data of sound and/or image signals and further of reproducing the recorded data at need, and it is manufactured as DVD-R, DVD-RW, or the like.
In an optical disk recording apparatus for DVR-R, DVD-RW, or the like, the optimization of the recording power is carried out, before actually recording desired information data, and this procedure is normally referred to as OPC (Optimum Power Control). The term “recording power” described hereinafter means the light emitting intensity of a laser diode (LD) as a light-emitting element in the state of forming pits for recording, and the laser diode is used for recording/reproducing the data in an optical disk. In the OPC, the recording power is varied in a plurality of steps in several sectors, e.g., 16 steps in 16 sectors, and a test data is recorded in a test area provided in a predetermined location of the optical disk. Thereafter, each test data is reproduced in a sector to evaluate its quality. Normally, either a beta value β or a modulation factor m is used as an evaluation index (parameter) for the quality of reproduction. Hereinafter, this value is represented as an evaluation index E.
The beta value β is a parameter which is derived from the peak voltage (A) and bottom voltage (B) of an envelope of an AC coupled reproduction RF signal as β=(A+B)/(A−B). The recording power is assumed to be optimum for the signal quality in the recording, when the beta value resides within a predetermined range (for instance, 0.04 to 0.05). The AC-coupled reproducing RF signal is an AC signal, which is obtained after the DC component is removed from the initial reproducing RF signal. The recording power, at which a desired beta value (reference beta value) may be obtained, is determined as an optimum recording power Pwo. Thereafter, all of the data are recorded at the optimum recording power Pwo thus determined.
The modulation factor m is a parameter which is derived from the peak voltage (A) and the bottom voltage (B) of an envelope of a reproduction RF signal having the DC component as m=(A−B)/A. The recording power is assumed to be optimum, when the modulation factor is within a predetermined range (for instance, 0.6 to 0.7). The recording power, at which a desired modulation factor (reference modulation factor) may be obtained, is determined as an optimum recording power Pwo. Thereafter, all of the data are recorded under the condition of the optimum recording power Pwo thus determined.
In Japanese Unexamined Patent Publication No. 7-85494, a method for determining the optimum recording power is described, in which a first beta value less than a desired beta value and a second beta value greater than the desired beta value are initially determined, and an apparent power step, in which the desired beta value can be obtained, is determined from the power steps in which the first and second beta values are obtained, using the direct approximation or the like, so that the recording power in the power step closest to the apparent power step is determined as the optimum recording power.
Moreover, in an optical disk recording apparatus for an optical disk such as DVD-RW, the eliminating power is further used. The eliminating power described herein means the intensity of light emitted from LD in the state of eliminating the recorded data. The optimum eliminating power Peo is determined from the optimum recording power Pwo according to a formula Peo=εo·Pwo, using a coefficient εo(the ratio of the eliminating power to the recording power) stored in a microcomputer built in the optical disk recording apparatus, or a coefficient εo recorded as ATIP (Absolute Time In Pre-groove) information in the optical disk.
There are various types of optical disks used for recording and reproduction. Moreover, the recording property and the production quality of the optical disk are different from disk to disk, so that the value of the reference evaluation index is also different from disk to disk. The optimum recording power can be determined using a preset evaluation index having a known value (e.g., for the beta value β=0.04 or for the modulation factor m=0.6). However, since the reference evaluation index is different from disk to disk, the recording power thus determined dose not always provide the best recording quality. In fact, there is a possibility that the recording power may be set on the basis of the evaluation index greater than the optimum evaluation index inherent in the disk. In this case, since the recording is carried out using a recording power greater than the optimum recording power, the layer for recording in the optical disk deteriorates and there is a possibility of greatly reducing the rewriting durability of the optical disk.
On the other hand, it is possible that a table is pre-installed in a microcomputer built in an optical disk recording apparatus and each disk medium maker calculates reference evaluation indexes and stores them in the table. In this case, the process of manufacturing the apparatus becomes complicated. If an optical disk having no reference evaluation index is inserted into the apparatus, it is impossible to carry out the suitable action.
In the case of optical disk recording apparatuses (disk drives) manufactured by same maker, even if the evaluation index is calculated with the same optical disk, the calculated value of the evaluation index is different form optical disk recording apparatus to optical disk recording apparatus due to a distribution in the wavelength of LD (laser diode) used in a optical pickup unit, a difference in the optical property thereof and an error in the accuracy of calculation in the circuit of determining the evaluation index. Therefore, even if a combination of a disk drive and an optical disk provides an optimum recording power at a reference evaluation index (for instance, beta value β=0.04 or modulation factor m=0.6), an optimum recording quality cannot always be obtained using the other disk drive and the same reference evaluation index.
It is possible that the calculation error of the evaluation index for each optical disk recording apparatus is determined in advance in the course of manufacturing the respective apparatuses and thereby the reference evaluation index for each disk medium maker is corrected. This procedure further provides a complicity in the treatment. A change in the recording property of the optical disk with the passage of time and a change in the optical property of the pick up unit cause the accuracy of correction to be reduced.